The present invention relates to a carbon article produced from the carbonaceous materials, and particularly to a large-size carbon article produced by calcining the mutually bonded pieces of carbonaceous material(s) and the method for bonding the pieces of carbonaceous material(s). More in detail, the present invention relates to an integrated carbon article of a large size having a bulk density of more than 1.01 g/cm.sup.3, produced by bonding pieces of carbonaceous material(s) of the same or different quality and flexible graphite sheet(s) interposed between each of the pieces of carbonaceous material(s), with an adhesive agent, and calcining the thus bonded material at a temperature of not lower than 800.degree. C., thereby integrating the thus bonded materials into a carbon article, the method for producing the same and the method for bonding the pieces of the large-size carbonaceous material(s).
In recent years, the carbon articles essentially consisting of the carbonaceous materials such as carbon fibers and carbon particles have been used in various industrial fields such as electrodes for a fuel cell and an electrolyser, and with the development of technology and the increase of demands, the requirements for the improvements of productivity and physical properties thereof have been increased more and more.
Although the carbonaceous materials are excellent in the physical properties, for instance, corrosion resistance, electro-conductivity, mechanical strength, etc. as the material, for utilizing these excellent physical properties more effectively, the study and development of carbon article produced by calcining composite carbonaceous materials obtained by bonding the carbonaceous materials of the same quality or the different quality has been conducted.
Such a carbon article has been hitherto produced by adhering a plurality of carbonaceous materials to each other with an adhesive agent and calcining and carbonizing the thus adhered composite carbonaceous materials. However, in the case of producing the composite carbonaceous material according to the just-mentioned process, there are cases where the carbonaceous materials once adhered together are separated from one other at the adhered surfaces thereof during the calcination due to the difference between the rates of expansion and contraction of the carbonaceous materials and those of the adhesive agent, and cases where cracks are formed in the thus produced carbon article, thus resulting frequently in the reduction of productive yield.
In addition, the demands for supplying the carbon articles of a relatively large size and/or of a complicated shape have been increased in recent years from the structural and functional view points, and in such cases, the problems of the above-mentioned separation (exfoliation) and formation of cracks become serious, particularly in the production steps.
As has been stated, the following strict demands have been imposed on the final products (the carbon articles). (1) Exfoliation of the once bonded pieces of carbonaceous material does not occur. (2) Cracks are not formed in the final product. (3) The final product retains the excellent specificities originally possessed by the carbonaceous material itself such as mechanical strength and electrical specificities. Namely, the production of the final product (the carbon articles) has been attended with much difficulty.
In consideration of the above-mentioned situations, the present inventors have studied for finding out the method of bonding the pieces of carbonaceous materials to each other to form the composite carbonaceous materials, and as a result of their studies, it has been found out that in the case of interposing flexible graphite sheet(s) obtained by compressing the expanded graphite particles, between the each piece of carbonaceous materials, bonding each of the pieces of the carbonaceous materials and the flexible graphite sheet with an adhesive agent and calcining the thus bonded material, the carbon article of the favorable specificities particularly for an electrode used in a fuel cell or in an electrolyser can be produced with a desirable productivity by the action of the flexible graphite sheet as the buffering layer of the carbonaceous materials having difference in the rates of thermal expansion and contraction between each of the pieces of carbonaceous materials, and the present invention has been attained based on the finding.
Namely, the object of the present invention is to provide a process for producing an integrated carbon article, particularly of a large size, which does not show the abovementioned demerits of the conventional technology for producing the carbon articles. In addition, another object of the present invention is to provide an integrated carbon article of a large size and of excellent specificities, produced by the above-mentioned process.